Many modern devices, such as high-energy lasers and high powered-lamps like solar simulator lamps, are capable of putting out high levels of energy in the form of radiation. In certain circumstances, it is desirable to capture and absorb all or part of the output beam of such devices. For example, capturing a portion of the output beam may be desirable when the full output of the device provides too much energy for a desired application. Whether capturing all or part of a beam, if such a device simply captures and absorbs the output energy it is referred to as a beam dump.
In other applications, it may be desirable to capture the output energy in order to measure the output level of the device. Such a measurement may be used to verify a manufacturer's claimed output levels for a device or to verify the performance of new devices and designs. In this case, the radiation capturing, absorbing, and measuring device is used as a calorimeter or power meter.
The body of the calorimeter captures and absorbs the radiation, and causes the temperature of the body to rise. Precise knowledge of the thermal capacitance of the body allows the user to correlate the temperature rise of the calorimeter body to the energy absorbed. Thus, an accurate measurement of the temperature rise of the calorimeter body yields the energy content of the radiation. Care must be taken that the heat loss of the body due to conductive, convective, and radiative cooling is minimized and/or well characterized. In order to make an accurate measurement of the energy in the input radiation, the calorimeter must be capable of surviving the radiation (which may be high power) and must absorb substantially all of the input energy.
Most currently available calorimeters must be cooled to survive high power radiation. Cooling prevents damage to the calorimeter. Cooling also resets the calorimeter to a condition in which the calorimeter is ready to make further measurements.
In most currently known calorimeters that are designed for high energy beam measurements, cooling and measuring are both effected by water that is pumped through channels in the body of the calorimeter. Energy, in the form of heat, is transferred from the body of the calorimeter to the water, thereby heating the water and subsequently cooling the body of the calorimeter. A precision thermometer of some type measures the temperature rise of the water and a flowmeter with substantial accuracy measures the flow rate of the water flowing through the channels of the calorimeter. The temperature rise of the water together with the measured flow rate of the water is used to approximate the energy absorbed by the calorimeter body.
However, currently known calorimeters that use water to measure the temperature change of the body include drawbacks. For example, in an attempt to accurately measure substantially all of the energy, the surface area available for heat transfer between the water and the calorimeter body is desired to be large. In order to accomplish this, numerous intricate water channels are machined into the body of the calorimeter. This increases surface area for heat transfer from the body of the calorimeter to the water, but this also introduces a pressure drop in the water flow because of constriction of the channels. Therefore, a high pressure pump is used to pump water through the numerous intricate channels. The high pressure pump itself is expensive.
Because the water channels are usually small and intricate, it is desirable to keep the channels free of corrosion and contamination. Corrosion and contamination within the channels can reduce the amount of heat transferred to the water or prevent water flow by blocking the channels. However, maintaining water chemistry within desirable limits to reduce contamination and corrosion introduces further costs because water chemistry maintenance is extremely labor-intensive. Moreover, deionized (DI) water is used as the cooling liquid and is treated with fungicide to further reduce corrosion. Use of DI water and fungicide increases costs even further. Further, if channel blockages become severe enough, there may be areas of the calorimeter that experience restricted water flow, thereby causing inaccurate measurement and/or elevated local temperatures at which the equipment may fail.
Inaccuracies in measurements are also introduced by pumping high-pressure water through intricate channels. For example, water is subject to self-heating due to the friction of the water being pumped at high pressure through the intricate channels. This unintended self-heating of the water results in a temperature rise in the water that is not caused by the input radiation and therefore is a source of inaccuracy in the measurement of input radiation.
Inaccuracies in measurement of water flow rates also cause inaccuracies in measurements of the input radiation. For example, when water is forced under high pressure to flow through the calorimeter body, it can set up turbulence in the flow that will introduce false readings in the flow meter.
Furthermore, there is some energy left in the calorimeter body that is not transferred to the water and therefore is not measured by the thermometer. This residual energy will then introduce inaccuracies in the measurement of the total energy of the radiation source.
As a result, there is an unmet need in the art for a high energy calorimeter that is able to withstand high power radiation, accurately measures substantially all of the energy of the radiation, and is inexpensive to fabricate, operate, and maintain.